Ancient Books Are More Than Stories — They’re Disease Archives
Tucked inside the vaults of museums and libraries around the world, centuries-old manuscripts have long been cherished for the words and illustrations they contain. But scientists are increasingly interested in something far less visible: the microscopic biological material embedded within the pages themselves. It turns out that parchment — the animal skin used to make many historical manuscripts — is a remarkable, if unintentional, archive of ancient pathogens, and researchers are only beginning to understand what it can tell us about the history of disease.
The field driving this research is paleomicrobiology, the study of ancient microorganisms recovered from historical materials. Combined with advances in ancient DNA (aDNA) analysis, scientists can now extract and sequence genetic material from parchment that is hundreds, sometimes thousands, of years old. What they’re finding is rewriting our understanding of how diseases evolved and spread across human and animal populations.
What Parchment Preserves — and How Scientists Extract It
Parchment is made primarily from the split skin of animals — most commonly sheep, calves, or goats. The manufacturing process, which involves soaking, stretching, and drying the hide, doesn’t fully eliminate the biological material embedded in the skin. Collagen, keratin, and crucially, fragments of DNA from both the animal and any pathogens it carried at the time of slaughter, can persist within the material for centuries under the right conditions.
In a landmark 2023 study published in Philosophical Transactions of the Royal Society B, researchers analyzing medieval parchments recovered ancient DNA from sheeppox virus (SPPV) — a pathogen in the same family as smallpox. The genetic material, extracted from manuscripts dating back several centuries, provided some of the oldest known genomic evidence of the virus. This discovery offered scientists a rare window into how poxviruses behaved and evolved long before modern veterinary records existed.
The extraction process is delicate. Researchers typically take tiny samples — sometimes just a few milligrams — from the edges or damaged portions of a manuscript to avoid destroying historically significant text. Using advanced sequencing technologies, they can reconstruct partial or even complete pathogen genomes from these minuscule fragments, cross-referencing them against modern viral databases to trace evolutionary lineages.
What Ancient Pathogens Can Tell Us About Modern Disease
The implications of this research extend well beyond historical curiosity. By comparing ancient pathogen genomes with their modern counterparts, scientists can calculate mutation rates, trace geographic spread, and identify when certain strains diverged. This kind of deep evolutionary timeline is almost impossible to construct from living populations alone.
In the case of sheeppox, the ancient DNA recovered from manuscripts helped researchers establish a clearer timeline for when the virus split from related poxviruses — information that could inform modern vaccine development and biosecurity strategies. Sheeppox and its close relative lumpy skin disease virus remain serious threats to livestock in parts of Africa, the Middle East, and Asia today, causing significant economic damage.
Parchment manuscripts also hold potential clues about human diseases. Researchers have detected traces of bacteria associated with anthrax (Bacillus anthracis) and brucellosis in historical animal hides, both of which can infect humans. Some scientists even hope that manuscripts from regions historically affected by plague might yield genomic data about early strains of Yersinia pestis, the bacterium responsible for the Black Death.
There are important caveats, of course. Contamination is a persistent challenge — modern DNA from handlers, conservators, and the environment can easily muddy results. Rigorous laboratory protocols and authentication methods are essential to confirm that recovered sequences are genuinely ancient rather than recent introductions.
A New Kind of Historical Document
It’s a remarkable reframing of what a manuscript actually is. For centuries, scholars have read parchment pages as linguistic and artistic records. Now, scientists are reading them as biological ones — each skin potentially carrying a molecular diary of the animal it came from and the pathogens circulating at the time.
As ancient DNA techniques become more refined and affordable, the number of manuscripts that can be analyzed will only grow. Libraries and archives hold millions of parchment documents worldwide, representing an enormous, largely untapped reservoir of paleopathological data. The books of the past, it turns out, may have as much to teach us about the future of disease as any modern laboratory sample.